Influence of the pressure, temperature, cation and anion on the volumetric properties of ionic liquids: New experimental values for two salts.

Abstract: Experimental densities of two ionic liquids (ILs), 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C₄C₁Pyrr][NTf₂]) and 1-(2-methoxyethyl)-1-methyl-pyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([C₁OC₂C₁Pyrr][(C₂F₅)₃PF₃]), were measured over a broad temperature and pressure range, i.e. from (278.15 to 398.15)K and up to 120MPa, respectively. The isobaric thermal expansion coefficient of the two ILs was determined from these measurements finding a non-monotonous behaviour over the entire pressure range. The density values obtained were used to analyse the prediction ability of the methods proposed by Gardas and Coutinho and by Jacquemin et al. Furthermore, the influence of the cation and anion structure on the densities and the isothermal compressibilities was analyzed, also considering literature values.